New rule!

[PenGwin]

Thanks gurus. I appreciate the input.



I will agree that it was no speedster on the highway, but thankfully it was strong enough to hold up to pretty steep mountain passes with no problem - though very slowly. We put in 8,000 miles traveling from Texas out to the West Coast and up through Oregon, Montana and Wyoming.


As apparently was to be expected, it was very slow going. That wasn't much of an issue as the scenery was beautiful (until the last 800 mile slog from the Panhandle back to San Antonio in the August heat...).


Am I right to suspect that a better gear ratio would give improved mileage? We averaged about 7-8 mpg over the course of the trip. Hard to pretend the eco-friendly solar could make up for that. I'm curious what those of you with more highway-focused ratios pull off.

[o1marc]

Lowering the number of the gear in the back will reduce the rpms at the same speed, so fuel economy is in order. I went from Butte to Coeur d'Alene at 85mph, got 7mpg, drop it to 65 and it's close to 10mpg.

[PenGwin]

Originally Posted by o1marc

Lowering the number of the gear in the back will reduce the rpms at the same speed, so fuel economy is in order. I went from Butte to Coeur d'Alene at 85mph, got 7mpg, drop it to 65 and it's close to 10mpg.

Jealous of your speeds and your mpg!



My bus was near to a gift, so I didn't look that horse (or rear axle ratio) in the mouth. Just took it and built it out and thankful we pulled it all off. At least now I can write a better and more honest for sale ad ...

[JustKip]

I wouldn't bet on gaining much fuel economy with the 366 (6.0L) GMC gas engine. It's currently geared for stop and go traffic around town, which means it should do well in the mountains too. Higher gearing (numerically lower) will reduce RPMs at a given speed, but won't help it on those mountain passes. In fact, you'll be more likely to need to downshift. You'll get a better highway cruising speed, but 8mpg is a good average for the 366 pushing a bunch of wind, with not much more than 10 being the top for flatland freeway cruising. But you'll be getting there faster for the same amount of fuel. It would be more of a fuel advantage with a diesel or bigger gas engine, where you'd have more torque for effortless cruising at higher speeds. The 366 was a great engine for its day, but it has its limits.

[cadillackid]

you got 8+ in a 366? thats damn good.. they normally dont do that well, granted its TBI which helped those out.. but thats a good MPG number..

[PenGwin]

Originally Posted by cadillackid

you got 8+ in a 366? thats damn good.. they normally dont do that well, granted its TBI which helped those out.. but thats a good MPG number..

Well let me be completely honest here: that 8 mpg (and never much of an 8+) was on the way DOWN the mountains! In the steep climbs we could get as low as 6 mpg. Flatlands we could hover a bit above 7 pretty easily. But on the way down out of those gorgeous highlands we could pull a solid 8 mpg.



Though I must admit I would just take Chuckles out of gear and let him coast ... otherwise the transmission was doing too much braking and that just didn't seem fair after making Chuckles work so hard getting up there in the first place.



I am a number nerd, especially when those numbers mean dollars, so over our 8,000 mile trip we ran 7.12 mpg. The lowest was on the way West when I was still learning to listen to the engine/transmission and figure out Chuckles' happy space; the best was on the way home when we were sliding from 9,000 ft above sea level to San Antonio's measly 650 feet above sea level (though it's so humid here we might as well be in the sea!)


So don't get too excited about that mpg ... we spent more on gas than anything else on our trip (though beer was a close second ). But thanks to solar power the beer stayed cold while we boondocked in national forests almost the entire trip.



I must say that while Chuckles is apparently not the HOLY GRAIL engine/transmission, he did provide us with one hell of a summer, and that would never have happened without the help I found on this forum.

[cadillackid]

7 makes sense.. I have an old 1978 International SV-392. and got about 6.6 on my cross country trip.. ( yes i am into the classic busses but not to convert)


the GMC 366 is a fantastic engine.. one of my favorites.. I never did let my bus coast down the hills.. to me thats hard on the brakes and hard on the trans to re-engage it at speed vs letting it help with braking...



my 1978 has the AT540 which doesnt brake real well but did my fine..



I have burned up to AT545s in other busses.. so I can say they arent the holy grail but they do fine for many people..
-Christopher